1. Field of the Invention
The present invention relates to synergistic antimicrobial compositions which are generally useful for inhibiting microbial growth wherever such microbial growth is found, e.g. in aqueous systems related to a wide variety of industrial applications. More particularly, the present invention relates to synergistic antimicrobial compositions of 1,2-dibromo-2,4-dicyanobutane (DBDCB) and at least one of the esters of parahydroxybenzoic acid. Methods for using the same are also disclosed.
2. Description of the Background Art
Both 1,2-dibromo-2,4-dicyanobutane (DBDCB), also known as 2-bromo-2-bromomethylglutaronitrile, and esters of parahydroxybenzoic acid, also known as parabens, are known individually as antimicrobial agents. The unexpected finding of the present invention is that they are synergistic when used in combination. As used herein, the terms "synergy" and "synergistic" refer to instances where the effectiveness of a composition comprising two or more biocides, such as DBDCB and at least one paraben, exceeds the sum of the efficacies of the individual components taken alone. Thus, using a synergistic biocidal combination may allow for use of a lower overall concentration of biocide or the realization of an enhanced antimicrobial effect at a comparable dosage.
U.S. Pat. Nos. 3,833,731, 3,877,922, 3,873,597, 3,644,380, 3,833,743, and 3,929,858 disclose DBDCB and its use as an antibacterial, antifungal, and algicidal agent. Compounds related to DBDCB are also effective as antimicrobial agents. For example, U.S. Pat. No. 4,442,122 describes the use of 1,2-dibromo-2-cycloalkane compounds to inhibit microbial growth, and U.S. Pat. No. 4,496,581 discloses 1,2-dibromo-2-cyano-2-(heterocyclic) alkane compounds and their use as antimicrobial agents.
The use of DBDCB and related compounds in conjunction with other antimicrobial agents is also known in the art. U.S. Pat. No. 4,830,657 describes a synergistic antimicrobial combination comprising DBDCB and 1,2-benzisothiazolin-3-one. U.S. Pat. No. 5,034,405 discloses use of admixtures of DBDCB, 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one as antimicrobial agents. U.S. Pat. No. 5,124,355 discloses an antimicrobial composition of DBDCB and 2-(decylthio) ethaneamine and a method of using the same. U.S. Pat. No. 5,364,874 discloses the antibacterial and antifungal activity of a biocidal combination containing 2-halo-2-halomethylglutaronitriles, including DBDCB, and 4,5-polymethylene-4-isothiazolin-3-one.
Likewise, esters of parahydroxybenzoic acid ("parabens") are known for their antimicrobial properties. For example, parabens are known as preservatives for cosmetic products, food products and pharmaceutical preparations. See, e.g., Orth, Handbook of Cosmetic Microbiology, p.88-91 (1993) (discussing the use of parabens as preservatives in cosmetic products, drugs and food); Steinberg, Cosmetics & Toiletries, 107, 77-78, 80, 82 (1992) (discussing use of parabens as cosmetic preservatives, both alone and in combination with other preservatives); and Cosmetics & Toiletries, 108, 47-48 (1993) (discussing the use of parabens as frequently used preservatives).
As used herein, the phrases "antimicrobial", "biocide", and "inhibiting microbial growth" refer to agents useful for the killing of, inhibition of, or the control of the growth of bacteria, yeast, fungi, and/or algae. A number of important industries have experienced serious adverse effects from the activity of such biological growth on the raw materials which they employ, in their process waters, on various components of their manufacturing processes, and in the finished products which they produce. Such industries include the paint, wood, textile, cosmetic, leather, tobacco, fur, rope, paper, pulp, plastics, fuel, oil, rubber, and machine industries.
It is contemplated that the synergistic admixtures of DBDCB and parabens disclosed herein, and the methods for using the same, will be useful in virtually any aqueous systems or on any article of manufacture in which inhibition of microbial growth is desired, absent compatibility problems. Important applications of the synergistic antimicrobial combinations of the present invention include, for example: inhibiting the growth of bacteria and fungi in aqueous paints, adhesives, latex emulsions, and joint cements; preserving wood; preserving cutting oils; controlling slime-producing bacteria and fungi in pulp and paper mills and cooling towers; as a spray or dip treatment for textiles and leather to prevent mold growth; as a component of anti-fouling paints to prevent adherence of fouling organisms; protecting paint films, especially exterior paints, from attack from fungi which occurs during weathering of the paint film; protecting processing equipment from slime deposits during manufacture of cane and beet sugar; preventing microorganism buildup and deposits in air washer or scrubber systems and in industrial fresh water supply systems; controlling microorganism contamination and deposits in oil field drilling fluids and muds, and in secondary petroleum recovery processes; preventing bacterial and fungal growth in paper coating processes which might adversely affect the quality of the paper coating; controlling bacterial and fungal growth and deposits during the manufacture of various specialty boards, e.g., cardboard and particle board; preventing sap stain discoloration on freshly cut wood of various kinds; controlling bacterial and fungal growth in clay and pigment slurries of various types which are manufactured for later use in paper coating and paint manufacturing and which are susceptible to degradation by microorganisms during storage and transport; as a hard surface disinfectant to prevent growth of bacteria and fungi on walls, floors, etc.; in swimming pools to prevent algal growth; and to control bacterial and fungal growth in various cosmetic products.
The synergistic antimicrobial compositions disclosed in the present invention are particularly applicable to slime control in papermaking processes. The control of bacteria and fungi in pulp and paper mill water systems which contain aqueous dispersions of papermaking fibers in various consistencies is especially important. The uncontrolled buildup of slime produced by the accumulation of bacteria and fungi causes off-grade production, decreased production due to down-time and greater cleanup frequency, increased raw material usage, and increased maintenance costs. The problem of slime deposits is especially critical in light of the widespread use of closed white water systems in the paper industry.
Another important area in which the antimicrobial compositions of the present invention are particularly useful is in the control of bacterial and fungal growth in clay and pigment slurries. These slurries comprise various clays (e.g., kaolin) and pigments (e.g., calcium carbonate and titanium dioxide) and usually are manufactured at a location separate from the end use application. This means that they are generally transported and stored for later use at the application site. Because of high quality standards for the paper and paint products in which such slurries are used, it is essential that these clay or pigment slurries have a very low microorganism count.
In addition, the synergistic combinations of the present invention and methods of using the same have been found especially useful in controlling the harmful effects of microorganisms in water or aqueous media. Systems which utilize circulating water or aqueous media become infected with microorganisms and experience substantial impairment of their efficiency when deposits of the microorganisms build up in the system. The deposits coat the walls of tanks and other vessels and any machinery or processing equipment which is employed and create blockages in pipes and valves. The deposits also create discolorations and other imperfections in the products being produced, forcing costly shutdowns. Control of microorganisms in aqueous media is particularly important where there are dispersed particles or fines in the aqueous media, e.g., dispersed cellulosic fibers and dispersed fillers and pigments in papermaking, and dispersed pigments in paint manufacture.
Accordingly, there remains a very real and substantial need for antimicrobial compositions capable of effectively controlling and/or inhibiting microbial growth in industrial aqueous systems and in articles of manufacture. Because of increasing environmental regulations, there is still a further need to provide biocidal compositions having enhanced antimicrobial effect which are effective in lower doses than historically used. Use of lower amounts of biocides has a favorable impact on the environment, and allows users to realize significant cost savings.